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Table Of Contents
IP Precedence and IP DSCP Marking
ATM Cell Loss Priority Bit Setting
Frame Relay Discard Eligibility Bit Setting
Related Features and Technologies
Supported Standards, MIBs, and RFCs
Configuring an IP Precedence Value
Changing an ATM CLP Bit Setting
Changing a Frame Relay DE Bit Setting
Verifying the Class-Based Packet Marking Feature
Configuring an IP Precedence Value Example
Configuring an IP DSCP Value Example
Configuring a QoS Group Value Example
Configuring a Classifying CoS Values Example
Changing the ATM CLP Value Example
Changing the Frame Relay DE Bit Value Example
Class-Based Marking
Note
This document only details Class-Based Marking. The document does not detail matching on packets based on these markings.
The previous version of this document included information related to matching based on packet marks (which are configured in class map configuration mode). The sections related to matching have been removed from this document.
If you need information regarding packet matching, see the Modular Quality of Service Command-Line Interface document. The Modular Quality of Service Command-Line Interface is an overview document that previews all aspects of the Modular QoS CLI, including packet matching.This document describes the Class-Based Packet Marking feature and includes the following sections:
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Feature Overview
Table 1 documents the history of this feature.
The Class-Based Packet Marking feature provides users with a user-friendly command-line interface (CLI) for efficient packet marking by which users can differentiate packets based on the designated markings. The Class-Based Packet Marking feature allows users to perform the following tasks:
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Note
In most cases, the purpose of a packet mark is identification. After a packet is marked, downstream devices identify traffic based on the marking and categorize the traffic according to network needs. This categorization occurs when the match commands in the traffic class are configured to identify the packets by the mark (for example, match ip precedence, match ip dscp, match cos, etc.). The traffic policy using this traffic class can then set the appropriate QoS features for the marked traffic. (For information on packet matching, see the note at the beginning of this feature module).
In some cases, the markings can be used for purposes besides identification. WRED and DWRED, for instance, can use the IP precedence or IP DSCP values to detect and drop packets. In ATM networks, the CLP bit of the packet is used to determine the priority of packet in a congested environment. If congestion occurs in the ATM network, packets with the CLP bit set to 1 are dropped before packets with the CLP bit set to 0. Similarly, the DE bit of a frame relay frame is used to determine the priority of a frame in a congested frame relay network. In frame relay networks, frames with the DE bit set to 1 are dropped before frames with the DE bit set to 0.
Packet marking is supported on interfaces, subinterfaces, and ATM virtual circuits (VCs). In an ATM PVC, a user can configure packet marking in the same traffic policy where he or she configures the queueing actions, on a per-VC basis.
IP Precedence and IP DSCP Marking
Marking a packet with an IP precedence or IP DSCP marking allows users to classify traffic based on an IP precedence or IP DSCP value, depending on which value is marked. These marking can be used to identify traffic within the network, and other interfaces can match traffic based on the IP Precedence or DSCP markings.
IP Precedence and DSCP markings are also used to decide how packets should be treated in Weighted Random Early Detection (WRED).
The IP DSCP value is the first 6 bits in the ToS byte, while the IP Precedence value is the first 3 bits in the ToS value. Therefore, the IP Precedence value is actually part of the IP DSCP value. For this reason, both values cannot be set simultaneously. If both values are set at the same time, the packet will be marked with the IP DSCP value.
If you need to mark packets in your network and all of the devices support IP DSCP marking and matching, use the IP DSCP marking to mark your packets, since the IP DSCP markings provide more packet marking options (64 individual values can be marked using IP DSCP marking, while only 8 individual values can be marked using IP precedence marking). If marking by IP DSCP is somehow undesirable, however, or if you are unsure if the devices in your network support IP DSCP values, use the IP precedence value to mark your packets. The IP precedence value is likely supported by all devices in the network.
A user can set up to 8 different IP precedence markings and 64 different IP DSCP markings.
QoS Group Value Marking
Marking a packet with a local QoS group value allows users to identify a group ID with a packet. The group ID can be used to classify packets into QoS groups based on prefix, autonomous system, and community string. This QoS group marking can only be used to classify traffic within a single router and cannot, therefore, be used to mark packets leaving the router. For this reason, QoS group values cannot be applied on output traffic policies (which are attached to interfaces using the service-policy output command).
The QoS group value is usually used for one of the two following reasons:
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A user can set up to 100 different QoS group markings.
CoS Value Marking
Marking a packet with a local CoS value allows users to associate a Layer 2 Class of Service value with a packet. The value can then be used to classify packets based on user-defined requirements. Layer 2 to Layer 3 mapping can also be configured by matching on the CoS value, since switches already have the capability to match and set CoS values. If a packet that needs to be marked to differentiate user-defined QoS services is leaving a router and entering a switch, the router should set the CoS value of the packet, since the switch can process the layer 2 CoS header marking.
The CoS value cannot be marked as part of an input traffic policy (which is attached to an interface using the service-policy input command). A CoS value marking can only be applied to output traffic policies (which are attached using the service-policy output command).
A user can set up to 8 different CoS markings.
ATM Cell Loss Priority Bit Setting
The ATM Cell Loss Priority (CLP) bit setting is used as a method for prioritizing the discarding of cells in congested ATM networks. A CLP bit has only one bit and can therefore only have two settings, 0 or 1. If congestion occurs in an ATM network, cells with a CLP bit setting of 1 are discarded before cells with a CLP bit setting of 0. Therefore, important ATM cells should be forwarded with the CLP bit set to 0, while less important ATM cells should be forwarded with the CLP bit set to 1.
ATM CLP bit setting is especially useful when a packet that left a Cisco router has been converted into an ATM cell. By default, the new cell has a CLP bit setting of 0. This setting can be changed using ATM CLP bit setting.
Frame Relay Discard Eligibility Bit Setting
The discard eligibility (DE) bit in the address field of a frame relay frame is used as a method for prioritizing the discarding of frames in congested frame relay networks. The frame relay DE bit has only one bit and can therefore only have two settings, 0 or 1. If congestion occurs in a frame relay network, frames with the DE bit set at 1 are discarded before frames with the DE bit set at 0. Therefore, important traffic should have the DE bit set at 0 while less important traffic should be forwarded with the DE bit set at 1.
The default DE bit setting is 0. The Class-Based Packet Marking feature allows users to change the DE bit setting to 1 for various traffic, giving users the option of keeping the default value of 0 or changing the value to 1. For this reason, users can use the frame relay DE bit marking to prioritize frames in a frame relay network.
Benefits
Network Partitioning and Categorizing
Packet marking allows you to partition your network into multiple priority levels or classes of service, as follows:
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A marking can be used to identify a packet for any class-based QoS feature (any feature available in policy map class configuration mode, although some restrictions exist).•
The QoS group value is usually used for one of the two following reasons:–
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Layer 2 to Layer 3 Mapping
If a packet that needs to be marked to differentiate user-defined QoS services is leaving a router and entering a switch, the router can set the CoS value of the packet, since the switch can process the layer 2 CoS header marking, and vice versa.
Weighted Random Early Detection Configuration
Weighted random early detection (WRED) uses IP precedence values or IP DSCP values to determine the probability that a packet will be dropped. Therefore, the IP precedence and IP DSCP markings can be used in conjunction with the WRED feature.
Improved Bandwidth Management in ATM Networks
The ability to set the ATM CLP bit allows users to extend their IP QoS policies into an ATM network. As congestion occurs in the ATM network, cells with the CLP bit set are more likely to be dropped, resulting in improved network performance for higher priority traffic and applications.
Improved Bandwidth Management in Frame Relay Networks
The ability to set the Frame Relay DE bit allows users to manage bandwidth in a frame relay network. As congestion occurs in a Frame Relay network, frames with the Frame Relay DE bit set are more likely to be dropped, resulting in improved network performance for higher priority traffic and applications.
Restrictions
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For information on CEF switching, consult the Cisco Express Forwarding section of the Cisco IOS Switching Services Configuration Guide.
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Related Features and Technologies
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Related Documents
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Supported Platforms
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Note
Therefore, the set atm-clp command is not supported on any platform that does not support these adapters. For more information, refer to the documentation for your specific router.
Supported Standards, MIBs, and RFCs
Standards
None
MIBs
The Class-Based Quality of Service MIB stores information about Modular QoS CLI features, including the Class-Based Marking features. This MIB is actually the following two MIBs:
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For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
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Prerequisites
CEF must be configured on the interface before class-based QoS packet marking can be used.
For information on CEF switching, consult the Cisco Express Forwarding section of the Cisco IOS Switching Services Configuration Guide.
Configuration Tasks
See the following sections for configuration tasks for the Class-Based Packet Marking feature. Each task in the list is identified as optional or required.
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To configure the Class-Based Packet Marking feature, you must either configure an IP precedence value or an IP DSCP value.
Configuring an IP Precedence Value
To mark a packet by setting the IP precedence bits in the ToS byte, use the following commands beginning in global configuration mode:
The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring an IP DSCP Value
To mark a packet by setting the IP DSCP value, use the following commands beginning in global configuration mode:
The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring a QoS Group Value
To associate a local QoS group value with a packet, use the following commands beginning in global configuration mode:
The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring a CoS Value
To mark a packet with a specific CoS value, use the following commands beginning in global configuration mode:
The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Note
Changing an ATM CLP Bit Setting
To set the CLP bit to 1 on all packets matching a specified class, use the following commands.
This command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Changing a Frame Relay DE Bit Setting
To change the Frame Relay DE bit from the default value of 0 to 1 on classified traffic using the Modular QoS CLI, enter the following commands:
This command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Verifying the Class-Based Packet Marking Feature
To verify the Class-Based Packet Marking feature and display the configuration of a policy map and retrieve information regarding QoS packet marking features that are configured in policy map configuration mode, use the show policy-map [interface [interface-spec [input | output [class class-name]]]] command in EXEC mode.
Configuration Examples
This section provides the following configuration examples:
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Configuring an IP Precedence Value Example
In the following example, a service policy called policy1 is created. This service policy is associated to a previously defined classification policy through the use of the class command. This example assumes that a classification policy called class1 was previously configured.
In this example, the IP precedence bit in the ToS byte is set to 1.
Router(config)# policy-map policy1 Router(config-pmap)# class class1 Router(config-pmap-c)# set ip precedence 1The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring an IP DSCP Value Example
In the following example, a service policy called policy1 is created. This service policy is associated to a previously defined classification policy through the use of the class command. This example assumes that a classification policy called class1 was previously configured.
In the following example, the IP DSCP value in the ToS byte is set to 5.
Router(config)# policy-map policy1 Router(config-pmap)# class class1 Router(config-pmap-c)# set ip dscp 5Router(config-pmap-c)# class class2 Router(config-pmap-c)# set ip dscp efAfter you configure the settings shown for voice packets at the edge, all intermediate routers are configured to provide low latency treatment to the voice packets, as follows:
Router(config)# class-map voiceRouter(config-cmap)# match ip dscp efRouter(config)# policy qos-policyRouter(config-pmap)# class voiceRouter(config-pmap-c)# priority 24The service policy configured in this section is not yet attached to an interface. This action is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring a QoS Group Value Example
In the following example, a service policy called policy1 is created. This service policy is associated to a previously defined classification policy through the use of the class command. This example assumes that a classification policy called class1 was previously configured.
In the following example, the QoS group value is set to 4.
Router(config)# policy-map policy1 Router(config-pmap)# class class1 Router(config-pmap-c)# set qos-group 4The service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Configuring a Classifying CoS Values Example
In the following example, a service policy called policy1 is created. This service policy is associated to a previously defined classification policy through the use of the class command. This example assumes that a classification policy called class1 was previously configured.
In the following example, the CoS value is set to 5.
Router(config)# policy-map policy1 Router(config-pmap)# class class1 Router(config-pmap-c)# set cos 5Changing the ATM CLP Value Example
In the following example, a service policy called policy1 is created. This service policy is associated to a previously defined classification policy through the use of the class command. This example assumes that a classification policy called class1 was previously configured.
In this example, all packets with IP precedence values of 0 or 1 are sent with the CLP bit set to 1:
Router(config)# policy-map policy1Router(config-pmap)# class atm-discardRouter(config-pmap-c)# set atm-clpThe service policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Changing the Frame Relay DE Bit Value Example
In the following example, a traffic policy called policy1 is created. This traffic policy is associated to a previously defined traffic class through the use of the class command. This example assumes that a traffic class called class1 was previously configured.
In this example, all packets with IP precedence values of 0 or 1 are sent with the Frame Relay DE bit set to 1:
Router(config)# policy-map policy1Router(config-pmap)# class fr-discardRouter(config-pmap-c)# set fr-deThe traffic policy configured in this section is not yet attached to an interface. This command is applied when you attach a service policy to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Command Reference
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
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Note
set atm-clp
To control the cell loss priority (CLP) bit setting on Cisco routers, use the set atm-clp command when configuring a policy map.
set atm-clp
Syntax Description
This command has no arguments or keywords.
Defaults
The CLP bit is automatically set to 0 when Cisco routers convert packets into ATM cells for ATM networks.
Command Modes
Policy map class.
Command History
12.0(7)S
This command was introduced.
12.1(5)T
This command was introduced on Cisco IOS Release 12.1 T.
Usage Guidelines
To disable this command, remove the service policy from the interface.
Examples
The following example illustrates a CLP bit set using the set atm-clp command in the policy map:
Router(config)# class-map ip-precRouter(config-cmap)# match ip precedence 0 1Router(config-cmap)# exitRouter(config)# policy-map atm-clp-setRouter(config-pmap)# class ip-precRouter(config-pmap-c)# set atm-clpRouter(config-pmap-c)# exitRouter(config-pmap)# exitRouter(config)# interface atm 1/0/0Router(config)# service-policy output bearRelated Commands
set cos
To set the Layer 2 CoS value of an outgoing packet, use the set cos command in policy-map class configuration mode. To remove a specific CoS value setting, use the no form of this command:
set cos cos-value
no set cos cos-value
Syntax Description
cos
Specifies matching of IEEE 802.1Q/ISL Class of Service values.
cos-value
Specific IEEE 802.1Q Class of Service value. The cos-value is between 0 and 7.
Defaults
Disabled
Command Modes
Policy map class configuration
Command History
Usage Guidelines
CoS packet marking is only supported in the CEF-switching path.
The set cos command should be used by a router if a user wants to mark a packet that is being sent to a switch. Switches can leverage Layer 2 header information, including a CoS value marking.
The set cos command can only be used in service policies that are attached in the output direction of an interface. Packets entering an interface cannot be set with a CoS value.
The match cos and set cos commands can be used in conjunction to allow routers and switches to interoperate and provide Quality of Service based on the CoS markings.
Layer 2 to Layer 3 mapping can be configured by matching on the CoS value, since switches already have the capability to match and set CoS values. If a packet that needs to be marked to differentiate user-defined QoS services is leaving a router and entering a switch, the router should set the CoS value of the packet, since the switch can process the layer 2 header.
Examples
In the following example, the cos-set policy map is created to assign different Classes of Service for different types of traffic. This example assumes that the class maps voice and video-data have already been created.
Router(config)# policy-map cos-set
Router(config-pmap)# class voice
Router(config-pmap-c)# set cos 1
Router(config-pmap-c)# exit
Router(config-pmap)# class video-data
Router(config-pmap-c)# set cos 2
Router(config-pmap-c)# exit
Router(config-pmap)# exitThis command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Related Commands
set fr-de
To change the DE bit setting in the address field of a frame relay frame to 1 for all traffic leaving an interface, use the set fr-de policy map class command. To disable the set fr-de policy map class command, use the no set fr-de command.
set fr-de
no set fr-de
Syntax Description
This command has no arguments or keywords.
Defaults
The DE bit is usually set to 0. This command changes the DE bit setting to 1.
Command Modes
Policy map class
Command History
Usage Guidelines
To disable this command in a traffic policy, use the no set fr-de command in policy map class configuration mode of the traffic policy.
If the DE bit is already set to 1, no changes will be made to the frame.
Examples
The following example illustrates a DE bit that was set using the set fr-de command in the traffic policy:
Router(config)# class-map ip-precRouter(config-cmap)# match ip precedence 0 1Router(config-cmap)# exitRouter(config)# policy-map atm-clp-setRouter(config-pmap)# class ip-precRouter(config-pmap-c)# set fr-deRouter(config-pmap-c)# exitRouter(config-pmap)# exitRouter(config)# interface atm 1/0/0Router(config)# service-policy output bearRelated Commands
policy-map
Specifies the policy map to which the class belongs.
show policy-map
Displays information about the policy-map for an interface.
set ip dscp
To mark a packet by setting the IP differentiated services code point (DSCP) in the type of service (ToS) byte, use the set ip dscp policy map configuration command. To remove a previously set IP DSCP value, use the no form of this command.
set ip dscp ip-dscp-value
no set ip dscp ip-dscp-value
Syntax Description
Defaults
No default behavior or values.
Command Modes
Policy map configuration
Command History
Usage Guidelines
Once the IP DSCP bit is set, other quality of service (QoS) services can then operate on the bit settings.
You cannot mark a packet by the IP precedence with the set ip precedence command and mark the same packet with an IP DSCP value by entering the set ip dscp command. If you are unsure of which method of marking to utilize, utilize IP precedence marking when your
The network gives priority (or some type of expedited handling) to marked traffic. Typically, you set IP precedence at the edge of the network (or administrative domain); data then is queued based on the precedence. Weighted fair queueing (WFQ) can speed up handling for high-precedence traffic at congestion points. Weighted random early detection (WRED) ensures that high-precedence traffic has lower loss rates than other traffic during times of congestion.
Reserved keywords such as EF, AF11, AF12 and so on can be specified instead of numeric values.
Examples
In the following example, the IP DSCP ToS byte is set to 8 in the policy map named policy1:
Router(config)# policy-map policy1 Router(config-pmap)# class class1 Router(config-pmap-c)# set ip dscp 8All packets that satisfy the match criteria of class1 are marked with the IP DSCP value of 8. How packets marked with the IP DSCP value of 8 are treated is determined by the network configuration.
After you configure the settings shown for voice packets at the edge, all intermediate routers are then configured to provide low latency treatment to the voice packets, as follows:
Router(config)# class-map voiceRouter(config-cmap)# match ip dscp efRouter(config)# policy qos-policyRouter(config-pmap)# class voiceRouter(config-pmap-c)# priority 24The set ip dscp command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Related Commands
set ip precedence
To set the precedence value in the IP header, use the set ip precedence policy map configuration command. To leave the precedence value as is, use the no form of this command.
set ip precedence ip-precedence-value
no set ip precedence
Syntax Description
Defaults
This command is disabled by default.
Command Modes
Policy map configuration
Command History
11.0
This command was introduced.
12.0(5)XE
This command was introduced in the modular quality of service (QoS) command-line interface.
Usage Guidelines
Once the IP precedence bits are set, other QoS services such as weighted fair queueing (WFQ) and weighted random early detection (WRED) then operate on the bit settings.
The network gives priority (or some type of expedited handling) to marked traffic through the application of WFQ or WRED at points downstream in the network. Typically, you set IP precedence at the edge of the network (or administrative domain); data then is queued based on the precedence. WFQ can speed up handling for certain precedence traffic at congestion points. WRED can ensure that certain precedence traffic has lower loss rates than other traffic during times of congestion.
Examples
The following example sets the IP precedence to 5 for packets that satisfy the match criteria of class map class1:
Router(config)# policy-map policy1
Router(config-pmap)# class class1
Router(config-pmap-c)# set ip precedence 5All packets that satisfy the match criteria of class1 are marked with the IP precedence value of 5. How packets marked with the IP precedence value of 5 are treated is determined by the network configuration.
The set ip precedence command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface or to an ATM virtual circuit. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Related Commands
set qos-group
To set a group ID that can be used later to classify packets, use the set qos-group policy map configuration command. To remove the group ID, use the no form of this command.
set qos-group group-id
no set qos-group group-id
Syntax Description
Defaults
This command is disabled by default. No group ID is specified.
Command Modes
Policy map configuration
Command History
11.1 CC
This command was introduced.
12.0(5)XE
This command was introduced in the modular quality of service (QoS) command-line interface.
Usage Guidelines
This command allows you to associate a group ID with a packet. The group ID can be used later to classify packets into QoS groups based on prefix, autonomous system, and community string.
To display QoS group information, use the show ip cef command.
Examples
The following example sets the QoS group to 1 for all packets that match the class1 class map. These packets are then rate limited based on the QoS group ID.
Router(config)# policy-map policy1
Router(config-pmap)# class class1
Router(config-pmap-c)# set qos-group 1The set qos-group command is applied when you create a service policy in policy map configuration mode. This service policy is not yet attached to an interface or an ATM virtual circuit. For information on attaching a service policy to an interface, see the Modular Quality of Service Command-Line Interface document.
Related Commands
show policy-map interface
To display the configuration of all classes configured for all service policies on the specified interface or to display the classes for the service policy for a specific permanent virtual circuit (PVC) on the interface, use the show policy-map interface global configuration command.
show policy-map interface interface-name [vc [vpi/] vci]]
Syntax Description
